This module implements a SAX filter which adds line-numbers and
column-numbers to errors generated by SAX handlers further down the
pipeline. Written explicitly  so that XML::Validator::Schema could
blame the correct line of XML for validation failures.

NOTE: This module requires a SAX parser which correctly supports the
set_document_locator() call.  At present there is just one,
XML::SAX::ExpatXS.  If you've got a number of XML::SAX parsers
installed and you want to make sure XML::SAX::ExpatXS is used, do
this:

   $XML::SAX::ParserPackage = 'XML::SAX::ExpatXS';
